Production of isophorone



Patented Mar. 14, 1944 raonuc'rron or rsornoaona Seaver A. Ballard, Berkeley. and Vernon E.

Ham-y, El Cerrito, 09,111., assignors to Shell Development Company, San Francisco, Calif., a

corporation of Delaware No Drawing. Application May 31, 1941, Serial No. 396,192

9 Claims.

This invention relates broadly to an improved process for the production of cyclic, mono-olefinic ketones from aliphatic ketones. More particularly, the invention is concerned with a method for manufacturing isophorone from acetone.

It is an object of the invention to provide an improved process for condensing and cyclizlng aliphatic ketones to produce cyclic, mono-olefinic ketones; Another object resides in providing a method which gives high yields of the cyclic ketones and is readily adaptable to the technical scale manufacture of such substances. A further object is to provide an improved process for the production of isophorone from acetone.

These and other objects will be apparent from the description of the invention given hereinafter. a

Acetone may be condensed and cycllzed to isophorone by heating in the liquid phase in the presence of an aqueous solution of an alkali metal hydroxide at a temperature of about 100 C. or higher. However, a number of by-products are produced by this method. Although isophorone is the principal reaction product, a 1055,

of yield of isophorone occurs owing to formation by side reactions of mesityl oxide, diacetone alcohol, phorone, and condensation products higher boiling than isophorone. The by-products formed, besides causing a loss of yield of iso- 80 phorone, are sometimes troublesome to dispose of in large scale commercial operation of the process since the proportion of the various by-products is substantially fixed by the operating conditions and may not be widely varied to meet market demands.

We have discovered an improvement in the process which enables the formation of by-products of lower boiling point than the isophorone to be limited or substantially suppressed. The 40 improvement comprises adding these by-products to the reaction mixture and conducting the desired condensation reaction in the presence of such added substances.

In the case of liquid phase, high temperature condensation of acetone to isophorone, the major by-product is ordinarily mesityl oxide. Diacetone alcohol is also formed, though in lesser proportions, as are by-products containing more carbon atoms than the desired product, isotion mixture, the production of these compounds 66 is suppressed or limited with a corresponding increase in the yield of isophorone. If desired, the proportion of added by-products may be such that the reaction mixture is in a state of substantial chemical balance with respect to these substances. In other words, the amount-of the byproducts added to the reaction mixture before occurrence of the desired reaction to isophorone may be in a quantity which is the same as that obtained from the reaction mixture after the reaction, with the result that the overall production of the added by-products is substantially nil for the process. In, some cases, it may be desirable to suppress the formation of only .one of the by-products by adding just this single substance to the reaction mixture. In other cases,'two or more of the by-products may be added to limit additional formation of these substances in the reaction mixture. Since mesityl oxide is usually the by-product obtained in largest proportion from the reaction mixture, the greatest increase in yield of the isophorone is ordinarily obtained by adding this compound to the reaction mixture to suppress further formation thereof.

While the principle of the invention is described with particular reference to the production of isophorone from acetone, this is done merely for convenience and it is to be understood that it is equally applicable to the production of other mono-oleflnic, cyclic ketones from other ketones. By mono-oleilnic, cyclic ketones'reference is made to isophorone and to homologues thereof which are known to the art as homo-isophorones. These compounds may be prepared from a variety of ketones, it only being necessary that the reactant be a ketone wherein one of the carbon atoms which is linked directly to the carbonyl group contains at least one hydrogen atom linked directly thereto and the other carbon atom contains at least two hydrogen atoms linked thereto. Representative reactants include, be-

sides acetone, such compounds as methyl ethyl ketone, methyl propyl-ketone, methyl isopropyl ketone, diethyl ketone, methyl isobutyl ketone. ethyl propyl ketone, ethyl isopropyl ketone, methyl benzyl ketone, cyclopentanone, cyclohexanone, and the like. Largely because of greater reactivity, apreferred group of reactants are the methyl ketones which contain a carbon atom, other than that of the methyl group, linked directly to the carbonyl group to which is linked directly at least one hydrogen atom.

The conversion of the treated ketone to a cyclic mono-olefinic ketone is eifected with the aid of an aqueous solution of an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, etc. In order that good reaction rates may be realized, it is desirable that the aqueous solution of hydroxide contain at least per cent of the hydroxide. The preferred concentration is one between about and 50 per cent.

One 01' the controlling factors in eifecting the condensation and cyclization of the ketone to a mono-oleilnic, cyclic ketone is the temperature. By heating the reaction mixture containing the aqueous solution of an alkali metal hydroxide and the ketone together with added by-products of lower boiling point thanthe mono-olefinic, cyclic ketone, the further formation of which it is desired to suppress, at a temperature of at least 100 C., the desired reaction is obtained. Ordinarily, temperatures between about 100 C. and 250 C. are suitable. Excessively high tempera-' tures at which decomposition of the product becomes appreciable, are, of course, to be avoided. Furthermore, since the reaction occurs in the liquid phase, such high temperatures require the use of inordinately high pressures on the reaction system. In order to maintain the reaction mixture in the liquid phase, the pressure applied to the reaction system is at least equal to the total vapor pressure of the reaction mixture at the reaction temperature. At the most preferred temperatures between about 140 and 170 0., when acetone is reacted to form isophorone, the pressure required to maintain the reaction mixture in the liquid phase ranges from about 150 to 250 pounds per square inch.

It is ordinarily desirable that the reaction mixture be composed of two liqigd phases; one comprising the aqueous catalyst solution and the other, the ketone mixture. By employing an aqueous solution of an alkali metal hydroxide containing at least 15 per cent of the hydroxide, the reaction mixture contains two liquid phases even with a ketone which is completely miscible with water like acetone. With two liquid phases present in the reaction mixture, the separation of the organic layer containing the desired product from the catalyst is simplified. Upon completion of the reaction operation, the organic layer may be withdrawn from the catalyst solution which may be used again for reaction of further material. When the reaction system consists of two phases, it is, of course, desirable that the reaction mixture be vigorously agitated during the course of the reaction to mix and bring into intimate contact the organic phase and the catalyst phase.

After separation of the organic layer from the catalyst solution, a small amount of the alkali metal hydroxide which may be present is neutralized, i. e, with a weak acid such as tartaric acid, and the unreacted reactant, product, and by-products are separated by distillation, extraction or other suitable methods. All or part of the by-produots of lower boiling point'than the produced cyclic ketone which are obtained from the distillation operation may be returned to the reaction system to suppress formation of these substances in further operation of the reaction system.

The condensation and cyclization of the ketories with an aqueous solution of an alkali metal hydroxide at high temperatures is particularly adapted to operation in a continuous manner. The ketone together with the desired amounts of lay-products is continuously fed to a reaction vessel fitted with a stirring means and heating means and containing an aqueous solution containing at least 15 per cent of an alkali metal hydroxide. Sufllcient pressure is maintained on the reactor to maintain the components of reac tion mixture substantially liquid. The reaction mixture is continuously withdrawn from the reactor and passed to a separator from which the catalyst solution is recycled to the reactor. The organic layer is continuously neutralized and distilled, the unreacted ketone and lower-boiling byproducts therefrom being recycled to the reactor while the mono-olefinic, cyclic ketone is removed from the system and further purified, if desired. In the case when acetone is the reactant, the contact time with the catalyst solution is adjusted so that the percentage of acetone con- 'verted is from about 10 to 25 per cent which may be from about 15 minutes to 1 hour. With other higher ketones, the contact times may be longer because of lesser reactivity, but very long contact times are to be avoided because the proportion of condensation products higher than the desired product becomes large. The ratio of the organic layer to the catalyst layer may be varied over wide limits. Ordinarily, for each volume of catalyst solution, about 0.5 to 5 of organic layer is suitable. It is desirable that the concentration of the hydroxide in the catalyst solution be maintained substantially constant. When acetone is reacted, the system soon reaches a steady state whereby the amount of water carried out by the organic layer is balanced by the water produced from the reactions. If it is desired that the catalyst concentration be maintained lower, this may be realized by adding water to the feed to the reactor. With the higher ketones which do not extract water so readily as does acetone, it may be desirable to employ an agent which will increase the solubility of water therein such as isopropyl alcohol in order to continuously extract the water of reaction from the aqueous phase.

In effecting the process of the invention, those by-products which are of lower boiling point than the mono-olefinic cyclic ketone are added to the reaction mixture. Furthermore, it is ordinarily desirable that these substances be added or recycled in essentially such proportion that the reaction system is maintained in a state of chemical balance with respect to these by-products.

The following examples are given for the purpose of further illustrating the invention.

Example I Acetone was condensed to isophorone in a steel autoclave equipped with stirring paddles. Cold acetone and an aqueous solution containing 20 per cent sodium hydroxide were charged to the autoclave in a ratio of 5 parts by weight of acetone to 4 parts of caustic solution. The mixture was rapidly heated to about 150 C., maintained at this temperature for three hours, and the autoclave cooled. The pressure during the reaction was about 160 lbs. per square inch. After cooling, the mixture was discharged from the autoclave and the two layers that formed were separated. The organic layer was washed with water until neutral and distilled. For each parts of acetone charged, the following amounts of products were obtained:

The yields of the products, based on the acetone converted, were:

Per cent Isophorone 39 Mesityl oxide 27.4 Diacet m 4.5 Heavy ends 11 Water of reaction 18 Example ll Example I was repeated exactly except that instead of using pure acetone as the initial charge, a mixture containing 95.2 per cent acetone and 4.8 per cent mesityl oxide wasemployed. It was found that for each 100 parts of the initial charge, there was obtained the following amounts of products:

Parts Acetone 83 Isophdrone 6.6 Mesityl oxide 4.7 Diacetone 0.7 Heavy ends 1.9 Water of reaction 3.1

Per cent Isophorone 54.1 Diacetone 5.! Heavy ends 15.6 Water of reaction 25.4

We claim as our invention:

1. In a process for the production of isophorone wherein acetone is heated with an aqueous solution of an alkali metal hydroxide at a temperature in excess of about 100 C. and under a pressure at least equal to the total vapor pressure of the reaction mixture at said temperature, the step which comprises substantially suppressing formation of mesityl oxide as a by-product by adding this compound to the reaction mixture in an amount sufficient to substantially maintain the reaction mixture in a state of chemical balance with respect to said compound. I

2. In a process for the production of isophorone wherein acetone is heated with an aqueous solution of an alkali metal hydroxide at a temperature in excess of about 100 C. and under a pressure at least equal to the total vapor pressure of the reaction mixture at said temperature, the steps steps which comprise separating diacetone alcohol from the isophorone produced and recycling the separated diacetone alcohol to the reaction.

4. In a process for the production 01' a monoolefinic, cyclic ketone wherein a methyl ketone in which the carbon atom, other than that of the methyl group, linked directly to the carbonyl group contains at least one hydrogen atom linked directly thereto is heated in the liquid phase with an aqueous solution of an alkali metal hydroxide at a temperature between about C. and 200 C., the steps which comprise separating lowerboiling organic by-products from the cyclic ketone produced and recycling said by-products to the reaction.

5. In a process for the production of a monoolefinic, cyclic ketone wherein a ketone in which one carbon atom linked directly to the carbonyl group contains at least two hydrogen atoms linked directly thereto and the other contains at least one is heated with an aqueous solution of an alkali metal hydroxide at a temperature above about 100 C. and under a pressure at least equal to the total vapor pressure of the reaction mixture at said temperature, the steps which comprise separating lower-boiling organic by-products from the cyclic ketone produced and recycling said by-products to the reaction.

6. A process for the production of isophorone which comprises continuously bringing acetone into contact in the liquid phase with an aqueous solution containing at'least 15 per cent sodium hydroxide at a temperature between about 100 C. and 250 C., continuously separating the organic layer from the catalyst solution layer, neutralizing entrained catalyst in the separated organic layer, separating mesityl oxide from said organic layer, and continuously recycling said mesityl oxide to the reaction mixture.

7. A process for the production of isophorone which comprises continuously bringing acetone into contact in the liquid phase with an aqueous solution containing at least 15 per cent of an alkali metal hydroxide at a temperature between about 100 C. and 250 C., continuously separating the organic layer from the catalyst solution layer, and continuously recycling to the reaction mixture by-products of lower boiling point than isophorone separated from said organic layer.

8. A process for the production of isophorone which comprises heating, in the liquid phase, acetone with an aqueous solution containing at least 15 per cent of sodium hydroxide at a temperature between about 100 C. and 250 C., and substantially suppressing formation of mesityl oxide as a by-product by adding this compound to the reaction mixture in an amount suflicient to substantially maintain the reaction mixture chemi-- cally balanced with respect to this by-product.

9. A process for the production of isophorone which comprises heating, in the liquid phase, acetone with an aqueous solution containing at least 15 per cent of sodium hydroxide at a temperature between about 100 C. and 250 C., and adding mesityl oxide to the reaction mixture in an amount effective to restrain formation of this substance.

SEAVER A. BALLARD. VERNON E. HAURY. 

